1. Field of the Invention
The present invention is related to clutches, and more particularly to a bi-directional overrunning clutch for controlling torque transmission to a primary drive axle of a working vehicle.
2. Background Art
Simple drive systems for two wheel drive working vehicles, e.g., lawn mowers, lawn vacuums, snow blowers, utility tractors, trimmers, edgers, concrete and asphalt cutters, and the like, typically include a drive shaft or belt connected to a single drive axle, which drives both drive wheels. The principal deficiency with this type of drive system is that the vehicle is inefficient during turning because the wheels rotate on a common shaft, and thus rotate at the same rate of speed.
For instance, when turning such a vehicle, the outer wheel must travel a greater distance than the inner wheel in the same amount of time. However, because the wheels rotate on a common shaft, the result is that differential rotation is not permitted, resulting in one of the wheels slipping or skidding. This slipping/skidding results in premature wear of the wheel, and damage to surfaces on which the vehicle is operating. A lawn mower with this type of drive system can damage the turf under the slipping wheel.
To eliminate this inefficiency, common drive systems for wheeled working vehicles generally provide a differential between the pair of drive wheels. The differential permits independent or differential rotation of the drive wheels on an axle when the vehicle turns. Differentials, however, have various disadvantages. For example, when one wheel losses traction with the ground, the conventional differential is unable to transmit torque to the opposite wheel. To address this problem, many differentials on the market today use some form of overrunning clutch, or differential lock, to transmit torque when needed to a driven shaft. One use of an overrunning clutch in an all terrain vehicle is disclosed in U.S. Pat. No. 5,036,939. In that patent, the vehicle incorporates overrunning clutches where the wheel hub mounts to the axle, thus allowing each wheel to independently disengage when required. Another use of an overrunning clutch in a differential is disclosed in U.S. Pat. No. 5,971,123, which describes an electromechanical, bi-directional overrunning clutch differential that addresses many of the problems inherent in the prior drive systems.
Another bi-directional overrunning clutch is described in U.S. Pat. No. 6,722,484 (hereinafter “the '484 patent”), which is hereby incorporated in its entirety by reference thereto. The bi-directional clutch of the '484 patent controls torque transmission to a primary drive axle through the use of a roller assembly, friction members and hubs. The bi-directional clutch of the '484 patent was designed and configured for use in light duty vehicles; e.g., snowblowers, lawnmowers, trimmers, etc. The '484 patent does not teach or suggest the use of such a bi-directional clutch in an integrated hydrostatic transmission (IHT). Nor does the '484 patent teach or suggest the use of such a bi-directional clutch in heavy-duty machinery, such as tractors, trucks, and other construction equipment, which require a more robust clutch configuration capable of withstanding higher stresses and loads than are typically encountered in light duty vehicles.